Astronomers from the European Southern Observatory have announced quite the find: a solar system 42 light years from us that harbors three super-Earths!

Edited to add: As noted in the comments, this artist’s illustration is pretty far off the mark! All three planets are so hot there is no way they could have water, so making them blue is scientifically inaccurate. I can’t believe I missed this when I first posted this entry and the picture!

The planets orbit the star HD 40307, a K-type star… meaning it’s slightly less massive, cooler, and a bit more orange than the Sun. Still, the planets are cooked; they orbit the star with periods of 4.3, 9.6, and 20.4 days, so they’re very close to the star itself. The surface temperatures of all three must be well over 1000 degrees Celsius. The planets are big, too, with masses of 4.2, 6.7, and 9.4 times that of the Earth. That makes them too small, as far as we know, to be gas giants like Jupiter and Saturn (which have masses of 100 or more times the Earth’s), though it doesn’t rule out these being small giants like Uranus and Neptune (roughly 15 and 17 times the Earth). Given their location so close to their star, it seems likely (though not for sure) that these are more like terrestrial planets, just a lot bigger — the biggest would have about twice Earth’s diameter.

So make no mistake. They’re kinda sorta like Earth, but they are not Earth-like. They’re not a nice place to visit, and you most certainly don’t want to live there.

The planets were found using the usual technique of looking for a wobble in the star as the planets tug on it gravitationally. That can’t be seen directly by looking at the star’s position; the motion is way too small for that. Instead, astronomers look at the spectrum of the star and measure the Doppler shift. As the planets pull on the star this way and that, the spectrum shifts, and that can be measured… though it’s very hard to do. That’s why the first planets detected in this way weren’t found until 1995*; coincidentally one of the astronomers on the team that found these planets, Michel Mayor, was on the original team to find the first planet orbiting another star like the Sun.

These findings were reported at a meeting in France for astronomers looking for such super-Earths. Two other extrasolar systems were announced there, too; one with a planet 9.5 times the Earth’s mass and the other with much more massive planets.

And so this raises the question: just how many stars are out there harboring planets? Even as we look at more and more stars, the fraction with planets seems to go up with every discovery, mostly because we’re getting pretty good at finding planets, including ones with smaller mass. And that takes us to the more important question: how many of these planets are like Earth? And that of course leads to the ultimate question: how many of them have begun receiving our transmissions of Doctor Who?

I mean, how many of them have life?

It’ll be a while yet before we know, but I think it’s a very, very cool thing that we’re looking.

*The first extrasolar planets were found orbiting a pulsar using a similar technique, but they are very very very very very unlikely to look anything like planets we’ve ever seen before!

It seems like the majority of exoplanets we find are large and close to their primary. Is that just an artifact of our planet-finding techniques? Obviously, wobble will be easier to see in the star when the planets are massive and close. Likewise, occultation would seem to work best with large planets.

Given the description of these planets, as you said, likely with “surface temperatures well over 1000 degrees Celsius”, I really don’t care for the “artist’s impression” in the image you provided, which shows atmospheric conditions and even indicates the presence of liquid water (based on the blue coloring between between the white cloud cover). I would think the presence of liquid water would be unlikely given the proximity to the star. The only thing about these planets that would be remotely like earth would be their relative size.

Maybe nit-picking, but looking at the picture certainly gives one a completely erroneous image of what such planets might actually be like. And it belies your description. Just my two cents.

I felt the same way about the artist’s depiction. Since these always are completely ficticious renderings, based more in fantasy than reality, the few things we do know about the planets should be reflected as accurately as possibly, if only to not get our hopes up for no reason.

The important thing about this discovery is that our ability to detect smaller exoplanets is expanding greatly. How awesome tree super earths on the same system the finding of an earthlike planet is just around the corner i can feel it..

It seems like the majority of exoplanets we find are large and close to their primary. Is that just an artifact of our planet-finding techniques?

Yes, most likely. You’re observation and explanation is spot on. We should continue to detect smaller and smaller planets as techniques and instruments become more sensitive.

That’s why I think if there is a technological civilization within a couple of hundred light years of Earth, they already know we’re here. We may have completed our own survey of planets out to 200LY within the next 100 years or so.

And so this raises the question: just how many stars are out there harboring planets?

The answer seems to be: many. Gas giants like Jupiter are relatively common around Sun-like stars, although hot Jupiters are strongly overrepresented among discovered planets (they’re not as common as more distant Jupiters). We know that Jovian planets are very rare around red dwarfs, but they have plenty of Neptune-mass planets. There is a big hole between Saturn and Neptune-mass planets (this is because of planetary formation), but when the mass is decreased from Neptune towards Earth-mass planets the number seems to go up fast. We haven’t seen many potential terrestrial planets yet, but this is because it is so hard to detect them. Indeed, we should be happy that we already know so many of them. The recent discovery of a super-Earth around a very low-mass star/massive brown dwarf suggests that even they can have planets, not to mention terrestrials.

You can bet that there are many, many terrestrials waiting to be discovered.

I can’t wait to start receiving and watching the alien version of Doctor Who! If the Drake equation can workout how many planets have life, what percentage of those planets would create a Doctor Who-type show??

Since the most productive method we have for finding these planets involves watching to see if the star wobbles from being tugged at by a planet in its orbit, then it may well be an artifact of our planet finding techniques. The easiest planets to find with this system would be really big planets orbiting very close to their stars. Finding something like Earth or Mars would be much harder. My understanding though is that the discovery of all these Hot Jupiters has really thrown a wrench into standard theories of planet formation.

how many of them have begun receiving our transmissions of Doctor Who?”

Just finished watching an episode of The Sarah Jane Adventures which I’d never seen before and once it finished and I cam here and saw that quote, it almost made me fall of my chair and I’m not sure why. ^^;

Well, I wrote the following as a comment to the Universe Today post about this (which has no info on likely surface temperatures, among other things), but I think it suits this one just fine. Who knows: maybe one of the artists doing these illustrations reads BAB and not UT:

Wow. Great news! I’m betting on the detection of an Earth-sized planet until the end of the decade.

I do, however, have an increasing beef with these “artist impressions”. Can the geometry of light and dark be any wronger?

And blue seas?! White clouds? At that distance from the star? These planets are scorching hot, way hotter than Venus or Mercury. Wereas they are probably massive enough to hold on to atmospheres, I’m guessing they would be severely depleted of hidrogen and other lighter elements. Plus they are probably tidally locked, which in itself would create atmospheric conditions completely different from any Earth equivalence.

If there’s anything certain regarding this illustration is that the actual system won’t look anything like it.

Still, three massive planets so close from the star and eachother would be quite a sight in eachother’s skies.

Bottom line is: please, do try not to mislead people with illustrations such as this one.

I heard a recent radio interview on NPR that asked the question (paraphrased): “How far away from Earth can you be before the strength of our television signals becomes lower than that of the cosmic background radiation (and hence buried in the static)?” The answer: Pluto.

I am direct decendant of Sir Christopher Wren. Among his many talents( apart from being the Architect of St Paul’s Cathederal) he developed an early form of sign language AND was a bit of an Astronomer too (member of the Royal Society etc etc) My favourite quote of his is:
“A time will come when men will stretch out their eyes. They should see planets like our Earth.”
Quite a prophecy for the 17th century. I love that his words are coming true
PS He also carved his name on the sarcen stones of Stonehenge but I will forgive him that piece of vandalism:)

Now, detecting one huge rocky planet around another sun, much less three, is sensational in it’s own right. But the phrase “Super Earths” makes one immediately think that these are worlds capable of supporting life as we know it. And unfortunately, a lot of people get their information just by skimming headlines and the first few sentences.

Just thought I would point out that there’s a great chance that these planets are only half-boiling hot.

Because they’re so close to the Sun, they’re most probably tidally locked, meaning that one side will be very very hot and irradiated, and the other one will be very, very cold, always facing away from the Sun.

I’ve got a brief writeup of it here, actually. But nice post; you did a great job on this story.

I should add that my previous comment does not apply to directed transmissions. Perhaps we should start beaming video feeds directly to some poor system? (In fact, I think the same NPR story reported that someone is, in fact, doing this already. on purpose.)

I believe that planets as well as life on other planets is a common occurence in the universe. People have a tendency to believe they are more spevial that they truly are, the perfect example of this is that they believe an omnipotent being actually hears they prayers and forgives their sins. Now that is self-confidence!

Back on topic, I believe that Earth-like planets are more common than we have understood this far. As astronomers grow increasingly skilled at finding smaller planets, I believe that this belief will be proven true.

Further, given that we have a water on a small rocky planet, in the goldilocks zone, is to me enough evidence of that we do not inhabit the only such planet in the universe. The odds proving this are too high to be ignored.

But then again, the mysteries of the universe will never ceaze to amaze us.

A question which I asked myself (being unable to answer) while skimming through the comments: Are all stars surrounded by planets, given how they are formed? The first generation of stars were only hydrogen, but subsequent generations have been born from clouds of dust that contained much more than hydrogen, right? Then, can it not be so that all non-first generation stars harbour planets of some sort, or perhaps planet(plut-)oids or asteroids?

I really don’t care for the “artist’s impression” in the image you provided, which shows atmospheric conditions and even indicates the presence of liquid water (based on the blue coloring between between the white cloud cover).

Maybe they’re trying to make up for all the red planets we used to see on the original Star Trek. You know, the ones they used to beam down to and find a gorgeous green earth-like environment with a blue sky.

You know what I would like to see, here for example, is a running score/total based on the Drake equation, using the number of planets we have found so far. Ok we would have to modify the equation somewhat, mainly (Ne) to include super earth’s. It could give us a idea of how well and fast we are progressing in the search for earthlike planets.

“Maybe they’re trying to make up for all the red planets we used to see on the original Star Trek. You know, the ones they used to beam down to and find a gorgeous green earth-like environment with a blue sky.”

I think that was a bit of subconscious wishful thinking about Mars, before the first probe was sent.

I know I’m a total nerd for saying so, but the increasing frequency of discoveries of terrestrial planets has me excited.. I’m going to break open a bottle of champagne when we find the first habitable one, because it will mean humanity’s chances of long-term survival went from zero to slim.

So lots of stars seem to have lots of planets. That’s mind-boggling by itself, but the real action may be on the moons of those planets (which we may never be able to detect?). If the MW contains 150B stars, and one in a hundred star systems each have three planets, and one in ten planets each have two moons, then there are nearly a billion moons out there in the MW.

If it’s more like one in ten star systems each have five planets, and those planets average five moons each, then we’re looking at 375 billion moons out there…

Btw, speaking to Josephine’s question, the same article claims that rotational velocity drops “abruptly” in the 90 % or so stars lower than F2 category, which could indicate planetary disks to share momentum with. I dunno if there are other mechanisms proposed. (But IIRC it was hard going for the disk hypothesis here, some electromagnetic coupling is involved to explain a difficult scenario, so what else could it be?)

PS. I had to add “Jupiters” to my spell checker. How old are those data bases anyway?

There’s nothing about these planets that resemble Earth, and I wish Phil Plait would not just pass on the misleading headline, but take control of the information and responsibility for what he says to his audience.

And the “super-Earth” thing, that’s how exoplanetary astronomers are calling the objects with masses between those of the Earth and those of Neptune, so that’s how Phil is and should be calling them. That’s the name that pops up in the literature, like it or not (and I don’t), much the same way we had a whole bunch of “jupiters” and “hot jupiters” dropped on us since the first exoplanets were discovered. Many of these planets – the hot jupiters especially – also have little resemblance to their namesake.

Besides, the effort put into categorization by planetary scientists is minimal. They just don’t care much in coming up with anything other than broad categories based in body mass and surface temperature. And that’s the way it should be, I guess, at least as long as we keep knowing so little about the properties of exoplanets.

The planetary classification effort I like the best isn’t even scientific: it’s science-fictional: The Planetary Classification List, spawned by the ArcBuilder’s guys. They have quite a few pretty good ideas in it, IMO, even if I don’t quite agree with other choices.

To clarify, these planets are simply “Earth-type,” in that they are rocky. They are massive as compared to our planet, and are scorched due to their close orbit. They simply cannot harbor life as we know it.

However, with telescopes coming with better resolution, we’ll be able to find planets in the habitable zones of stars.

And that of course leads to the ultimate question: how many of them have begun receiving our transmissions of Doctor Who?

BBC reused tapes that contained early Doctor Who episodes and because of that some episodes are lost. The only copies left are traveling in the interstellar space. Unless some alien is copying them, the only way to retrieve them is to have a faster than light spaceship. Such spacecraft could break causality, and if that can be done, then also time traveling should be possible. Somehow sounds appropriate.

…. SNIP ….. Btw, speaking to Josephineâ??s question, the same article claims that rotational velocity drops â??abruptlyâ?? in the 90 % or so stars lower than F2 category, which could indicate planetary disks to share momentum with. I dunno if there are other mechanisms proposed. (But IIRC it was hard going for the disk hypothesis here, some electromagnetic coupling is involved to explain a difficult scenario, so what else could it be?)

There are stars above this ‘rotation break’ which comes into play around mid spectral class F with protoplanetary disks (& evolved stars over this mass which started life as hot main-sequence A dwarfs but are now orange or red giants or sub-giants with planets – notably Pollux, Errai (Gamma Cepehi), Ain (Epsilon Tauri), Edasich (Iota Draconis) & HD 17092 b – the Jovian-type planet orbiting its orange giant star in 360 days which generated media interest for having an â??earth-likeâ?? orbit.

For examples, Vega (spectral class A0 V & so nearly a B-type dwarf), Fomalhaut (A3 V) and Beta Pictoris (A? V) all have protoplanetary disks that were detected back in the 1980’s and which were confirmed by later studies to be currently forming planets. Won’t swear to it but am pretty sure all those stars are (as is usual for spectral classes O,B,A & early F) rotating very rapidly.

For more info. I recomend checking out the stellar expert James B. Kaler’s website :

* Gliese 436 b : The first known â??Hot Iceâ?? type planet, it was discovered by transiting to have a 50,000 km diameter â?? too small for a gas giant, too large for a superEarth. Models suggest it has a water-rich composition with a steamy atmosphere then a superheated ocean forced by high pressures at depths into exotic types of â??hot ice.â?? It orbits an M2 red dwarf star, 33 ly off in 2 and 1/2 days

* HD 69830 : Triple â??exo-Neptunesâ?? system around a Sun-like star 42 ly distant in Puppis. These planets all roughly Neptune-mass have 8, 31 and 197 day orbits with a large asteroid belt also being detected in the system.

* Pollux & â??Polydeucesâ?? : Orange giant Pollux is the only first magnitude and brightest star (ranks 17th in our sky by apparent magnitude) with a known exoplanet â?? a superjovian with a circular 590 d. orbit. This exoplanet dubbed “polydeuces” after a variant of the star’s name has triple Jupiter’s mass.

* Ain (Epsilon Tauri) belongs to the Hyades cluster forming the other â??bullâ??s eyeâ?? â?? the meaning of its name in Arabic opposite Aldebaran in the â??Vâ?? shape â?? and unlike Aldebaran it is a true member of the Hyades located 155 light years away. Ain b was the first exoplanet found in an open cluster and the most massive star yet found with a planet â??2.7 solar masses. Its superjovian planet has at least 7 and a half Jovian masses and orbits in 595 days 1.9 AU from its gargantuan star.

* Er Rai or Gamma Cephei b : Before “Polydeuces” was found around Pollux, this was previously the brightest star with an orbiting exoplanet. Errai is a 3rd mag. yellow sub-giant 45 ly off with a 1.5 Jove mass exoplanet in an orbit equivalent to just beyond Mars position in our system. Only three other named stars have confirmed exoplanets : Pollux, Ain (Epsilon Tauri) and Edasich (Iota Draconis), all the latter being orange giants. Ain belongs to the Hyades cluster forming the other â??bullâ??s eyeâ?? in the â??Vâ?? opposite Aldebaran.

* HD 17092 b : Jovian-type planet orbiting its orange giant star in 360 days which generated media interest for having an â??earth-likeâ?? orbit. In reality, however, there is very little earth-like about it! For starters, the orbit is actually a bit further than Earthâ??s being about 1.3 AU given the greater (2.3 solar) mass of the star which consequently â??drivesâ?? the exoplanet along its orbit much faster. More importantly, this worldâ??s type of sun this is vastly different being a K0-type giant with a vastly greater diameter, surface area and luminosity. Calculations show this planets temperature would be around 500 degrees Celsius â?? hot enough to melt lead or zinc. Moreover, the exoplanet itself â??weighsâ?? over four Jupiter masses and is vastly different from being a rocky Earth-like planet! HD 17092 was the 10th orange or red giant star discovered to have planets orbiting it.

â??Hotter stars fuse hydrogen to helium through the carbon cycle (in which carbon is used as a nuclear catalyst) rather than directly, have no circulating convective outer layers, and also tend to rotate much faster (Alkalurops [Mu Bootis -ed.] spinning at least 40 times faster than the Sun). â??

â??… Lower-mass solar type stars rotate slowly (the sun taking 25 days at an equatorial speed of 2 kilometers per second), while high-mass stars rotate quickly. The division in rotation is rather sharp, the “rotation break” falling in the middle of class F. Anwar, rotating at least 76 kilometers per second (with a period under 1.4 days), falls just above the limit. Like the Sun, however, the rotation (and convection in its outer layers) give Anwar an X-ray-emitting hot corona. ”

MaDeR on 16 Jun 2008 at 1:03 pm :

Josephine, I think that planets are around most of stars. In other words, special conditions are required to NOT having planets (like being close to star of type O).

Actually, some of the most supermassive stars have had protoplanetary disks found around them notably two stars in the Large Magellanic Cloud had proto-planetarydisks discovered by the Spitzer telescope :

“These stars are so large that if they replaced our Sun in the centre of the solar system they would swallow whole Mercury, Venus, Earth and Mars.”

The accompanying illustration (a superb one which I’ve colour photocopied & used in talks!) showed a blue or white supergiant and planet-forming disk compared with our inner solar system. Such superlarge stars esp. if NOT redor yellow supergianst must be extremely massive stars with at least 10 and probably mor elike 20-120 solarmasses – putting their mass in the O-type dwarf and even hypergiant (Eg. P Cygni, Eta Carinae) range!

So it looks from that news like planetary formation runs from the largest to smallest of scale sand thatall spectral classes may be accompanied by planets …

Mind you, finding planets around such stars would be exceedingly difficult given such stars mind-boggling brightness and their high mass means it’ll be incredibly hard to detect any ‘wobble’ because their planets simply won’t have the comparative heft that Jovians or SuperJovians do against tugging smaller stars about …

PS. Sorry TorbjÃ¶rn Larsson, OM the computer seems to have stuffed up your name – I cut & pasted so it should’ve turned out alright .. but then the wretched machine also messed me about with apostrophes / quotes so .. argh! Anyway #@%^^!!^^*&&$% computers!

I’d imagine all these planets are molten or semi-molten rocks under deep layers of exotic hot high-pressure forms of ice perhaps beneath deep ocena sof pressurised chemicals and then smothered in thick atmospheres. I’d expect them to be tidally locked and perhaps with one super hot hemisphere and one super cold one -or perhaps the heat-flow is distributred by atmospheric winds makes the whole planet hellishly similar temperature-wise a la Venus .. But that’s my speculation on what these worlds may be & I’m hunble enough to admit we simply don’t know.

Earth-like? Not at all likely no.
Intriguing and worth thinking about? Definitely!
_____________________________

* Gliese 581 : Gliese 581c orbits near the stars habitable zone in 13 days, could be rocky and is among lowest mass exoplanets yet found – 5 earth masses. The star also has a 15 earth-mass Hot Neptune orbiting in 5 days & an outer 8 earth-mass exoplanet orbiting in 84 days. Despite considerable initial hype, later studies suggest Gliese 581c is more likely to be a hostile Neptune-Venus cross than anything resembling an “earth-like” habitable planet.

… & its done it once again (& again!) in the attempted correction. (Which also nearly fell foul of the spam filetr thingammy ..) Sigh.

Sorry.

BTW. Lets not forget we’ve now got quite a number of interesting low-mass systems with this trio of SuperVenus-cross-Neptunes, the trio of mini-Hot Neptune’s around HD 69830 & Gliese 581’s three low-mass SuperVenus x Neptunean planets.

I’d imagine these planets are :

– Molten or semi-molten rocks

– under deep layers of exotic hot high-pressure forms of ice;

– perhaps beneath deep oceans of pressurised chemicals

– and then smothered in thick atmospheres.

I’d expect them to be tidally locked; perhaps with one super hot hemisphere and another super cold one. Or perhaps the heat-flow is distributed by their atmospheres makin the whole planet hellishly similar temperature-wise a la Venus ..

But that’s my speculation on what these worlds may be & I’m hunble enough to admit we simply don’t know.

“I heard a recent radio interview on NPR that asked the question (paraphrased): “How far away from Earth can you be before the strength of our television signals becomes lower than that of the cosmic background radiation (and hence buried in the static)?” The answer: Pluto.

Bummer.”

This is a common misconception that our TV signals fade out to zero past some certain point. The distance at which the signal falls below background noise depends on the collecting area of the receiver. Thus, a more advanced extraterrestrial civilization can receive our TV signals and planetary radar signals out to a much greater distance than a relatively unadvanced civilization. I don’t have the equation in front of me but a really advanced civilization, say Kardashev Type II, might build a collecting area of millions of square kilometers. If so they could probably hear us from thousands of light-years away.

Here is some information on 8 exoplanets that may be in their star’s habitable zone. If you pick the correct albedo and greenhouse temperature increase then these exoplanets are within the circumstellar habitable zone of their star for their entire orbit. Some of the stars even have two planets that may orbit entirely within the habitable zone. In this case the definition of the habitable zone is that the average surface temperature of the planet is between 0 degrees and 50 degrees Celsius.

The search criteria are as follows:
albedo: from 0.15 to 0.85
greenhouse temperature increase: 0 to 100 degrees Celsius

The planetary classification effort I like the best isn’t even scientific: it’s science-fictional: The Planetary Classification List, spawned by the ArcBuilder’s guys.

With over 200 exoplanets being discovered to date something like the Harvard/Yerkes stellar spectral type classification must be developed for exoplanets. Probably as soon as a significant number of exoplanet spectra are measured it will be. I would like to propose the following classification system:

Class: R (rocky)
Description:
Crust composed primarily of silicate
Frozen water is an insignificant part of the crust
Well-defined surface no more than 500 km below cloud tops (if there is an atmosphere at all)

Class: I (icy)
Description:
Crust composed primarily of frozen water
Silicate is an insignificant part of the crust
Well-defined surface no more than 500 km below cloud tops (if there is an atmosphere at all)

# Kevin Whiteon 16 Jun 2008 at 4:04 pm wrote: “That’s mind-boggling by itself, but the real action may be on the moons of those planets (which we may never be able to detect?).”

Never be able to detect??

I don’t think so. When I was growing up, the prevailing wisdom was that we would not be able to detect planets orbiting other stars. The dim light of their reflection would be washed out by the intense glare of the star itself. Oh, and because of distance, we couldn’t actually go and take a closer look.

Well, not only have we found planets orbiting other stars, we’ve found a *lot* of them. And there are a whole *lot* more of them waiting to be discovered.

Most of the ones we have discovered are big and orbit close to the primary. Now we are starting to find smaller ones, and I figure it won’t be long before we start finding them further out from their parent stars.

Instead of planetary reflections beign completely washed out, we’ve started developing techniques to separate reflected light from the star’s light, and that’s telling us stuff about these exoplanet’s atmospheres.

I’ll dare venture that, if these planets have moons (and I’ll bet at least some of them do), it’s only a matter of time before we detect them.

The only question (for me anyway) is whether I will be around to see it, or whether I will have gone into a growth industry pushing up daisies.

Wouldn’t it be impossible to find moons using the prevailing planet-finding technique? It only measures the gravitational pull of a planet’s orbit on its sun. I would imagine that whatever figure we come up with for the mass of the orbiting planet includes its satellites.

The only way I can thing of to discover a moon in another solar system is to be lucky enough to catch a planet transiting its sun, and at that very moment a large moon transiting the planet.

Exceptionally unlikely but with satellites imaging hundreds of thousands of stars sooner or later it’ll happen.

Actually, the transit technique seems to be the most promising, as far as moons are concerned (or the only one that shows some promise). With low-mass and low-luminosity stars, we may be already capable to detect the transit of a large moon. The transit of the *star* by a large moon, I mean. Not the transit of the planet. That’s pretty much undetectable.

The problem with that is that the transit method is a whole lot better in detecting objects near the star than far away objects, and the closest a planet is to its star, the smaller its Hill sphere is and the less likely it is to have moons, especially big ones.

Since the planetary classification topic came up more in depth, here’s a link to the ArcBuilder’s PCL I mentioned earlier. There are a number of versions on the intertubes, but this one seems to be the most recent:

This is a common misconception that our TV signals fade out to zero past some certain point. The distance at which the signal falls below background noise depends on the collecting area of the receiver.

Let’s consider television signals. Let’s assume the transmission is UHF channel 14 which has a video carrier at 471.25 MHz. The brightness temperature of the sky at this frequency is quite high, about 30 deg K. If it’s an NTSC signal (United States standard) then Bt is about 6 MHz. Let’s let Br equal 6 MHz too and tau-r = 0.167 microseconds. Then SQRT(tau-r * Br) is 1.0.

Let’s assume a typical television station power of 50,000 watts and assume the worst case, that the signal is isotropic (spread out in all directions). We’ll assume that the signal to noise ratio equals 1.0. Let’s also assume that some kind of supercivilization is picking up the broadcast so the noise temperature of the receiver is almost to the cosmic background noise level of 2.7 deg K (let’s put it as 5 deg K).

“However, with telescopes coming with better resolution, we’ll be able to find planets in the habitable zones of stars.”

Not with the atmosphere getting in the way. RV precision is almost at the level of atmospheric distortion (if it’s not already there). The sooner we get Obama in office, the sooner we’ll be able to get the space missions going again, which, incidentally, have been put on hold because of all the money and resources being funneled away to satisfy Bush’s fetish of getting man on Mars.

So it would take a receiving dish of diameter 9,100 km to receive our TV broadcasts out to a distance of 1 light-year. To receive our full TV video and audio signal out to a distance of 1,000 light-years the receiving dish must have a diameter of 9.1 million km. This seems outlandish to us but it may very well be within the capabilities of an advanced extraterrestrial civilization.

If we consider only the audio portion of the signal then the bandwidth improves from 6.0 MHz to 10 kHz and the diameter of the dish needed to receive just the audio portion out to a distance of 1,000 light-years is 370,000 km.

Add a little directionality to the signal, say let the transmitting dish (upload to satellite) have a diameter of 10 meters with wavelength of 64 cm, then the diameter of the receiver needed shrinks to 7,500 km to pick up our TV audio out to 1,000 light-years, 750 km to pick up our TV audio out to 100 light-years, and 75 km to pick up our TV audio out to 10 light-years. Some of these receiver sizes might even be feasible for our civilization in the distant future. So yes, it is possible for an advanced ET to pick up our TV signals at great distances.

StevoR, thanks for the info. So we have even more stars with possible planets – but the rotation drop isn’t telling us anything. PS. The name thingie is OK; you can spell it Torbjorn and it’s still recognizable.